Auditory signal generator for people suffering from tinnitus

ABSTRACT

The invention concerns an auditory signal generator for reducing, or even eliminating tinnitus. The invention is characterised in that it comprises the following operational phases: a) measuring the absolute auditory thresholds; b) measuring the perceived frequency of tinnitus; c) calculating on the basis of the measurements obtained characteristics of an auditory signal adapted to a subject&#39;s particular case, so as to programme said generator enabling it to deliver, with appropriate means, said correcting signal.

[0001] The present invention relates to a process for programming adevice for generating auditory signals intended to be heard by peoplesuffering from tinnitus. It also relates to a device implementing such aprocess, of which the characteristics of the signals generated areadapted specifically to the audiological characteristics of anindividual in order to promote the disappearance or alleviation oftinnitus in this individual.

[0002] By tinnitus is meant the perception of noises in the ear or inthe head which do not correspond to any acoustic signal in theenvironment. The nature of these noises and the intensity with whichthey are manifested can vary according to the case. Generally, thenuisance caused by tinnitus can be considerable to the subject; it canbecome debilitating and lead to serious psychological disorders, inparticular mood and sleep disturbances. Moreover, most people who sufferfrom tinnitus also have a more or less serious hearing loss.

[0003] In a standard fashion, a person suffering from tinnitus isoffered different types of treatments, the actual effects of which arenot always conclusive. Pharmacology represents the most common method oftreatment, but none of the substances prescribed has any demonstratedbeneficial effect, and certain of them even have negative effects, tothe extent of aggravating the nuisance caused by the tinnitus.

[0004] There are also tinnitus-masking devices which are systemsdelivering a sound signal into a patient's ear, in order to render thetinnitus inaudible, either directly and immediately, by perceptualmasking, or progressively, by virtue of a process of physiologicalhabituation.

[0005] The tinnitus maskers proposed at present pose several problems:

[0006] the signal-generation possibilities of these systems are verylimited. In fact, in most cases, they do not make it possible to producea single type of signal with very simple spectral characteristics, whichconsiderably limits the possibilities of adaptation to the particularcase of each patient.

[0007] moreover, the existing maskers are generally presented in theform of hearing aids. This type of device puts off a number of tinnituspatients, especially the younger ones, who do not have sufficienthearing loss to need to wear a hearing aid, and do not wish to give theimpression of suffering from a handicap.

[0008] finally, the insufficient adaptability of these maskers to theparticular case of each tinnitus sufferer makes them ineffective andeven, in certain cases, aggravates the severity of the disorder.

[0009] The present invention thus aims to overcome these drawbacks byproposing a process for programming a device generating auditorysignals, the physical characteristics of which are adapted to theparticular case of a tinnitus sufferer: listening to them over a longperiod should lead to its final or temporary disappearance, or at thevery least alleviate the tinnitus and the nuisance associated with it.

[0010] To this end, the process for programming an auditory signalgenerator, which is a subject of the invention, with a view toalleviating, even eliminating tinnitus, is characterized in that thefollowing operational phases are carried out:

[0011] a) measurement of the absolute auditory thresholds,

[0012] b) calculation, on the basis of the measurements obtained, of thecharacteristics, also referred to as spectral envelope, of an auditorysignal adapted to a subject's particular case, in order to programmesaid generator allowing it to deliver said auditory signal, usingappropriate means.

[0013] The invention also relates to an auditory signal generatorallowing implementation of the process, comprising appropriate meansallowing it to deliver a corrective signal, comprising a device formultiplication of the spectral envelope with the spectrum of a whitenoise and inverse Fourier transform, for the purposes of direct use orfor the purposes of storage within a support.

[0014] Other characteristics and advantages of the present inventionwill appear from the following description, with reference to theattached drawings, which illustrate an embodiment thereof, without anylimiting character. In the figures:

[0015]FIG. 1 represents the different stages of a process forprogramming an auditory signal generator, according to the invention;

[0016]FIG. 2 diagrammatically represents the calculated form of thespectral envelope of the adapter-equalizer signal according to theinvention;

[0017]FIG. 3 is a representation on several levels of the auditorysystem of the neuronal responses caused by an adapter-equalizer signal;

[0018]FIG. 4 is a representation on several levels of the auditorysystem of the neuronal responses caused by a white noise;

[0019]FIGS. 5a, 5 b and 5 c represent the tonotopic organization of thecentral neurons in, respectively, a subject with normal hearing, asubject with tinnitus with hearing loss, and the same subject afterlistening to an adapter-equalizer signal.

[0020] According to a preferred method of implementation of the processaccording to the invention, said process for programming a sound-signalgenerator comprises 4 major distinct operational phases, and inparticular an intermediate stage between the main stages a and bcorresponding to the measurement of the perceived frequency of thetinnitus (FIG. 1):

[0021] In order to carry out the first stage and the intermediate stage,first and second means are used which can be identical. In particular,these first and second means can comprise a pure sound generator,logarithmic attenuators, a headphone preamplifier and a headphone.

[0022] A first operational phase (cf. stage a) consists of measuring theabsolute auditory thresholds. These thresholds, defined as being thelowest intensity of sound that the subject can perceive, are measuredusing pure sounds of different frequencies, the intensity of which canbe varied depending on the responses of the subject, who has the task ofindicating, by means of a response device (of push button or othertype), whether or not he can hear these sounds. In order to do this, anintermittent sound of given frequency and intensity is emitted by thefirst means into one of the subject's ears; the subject then indicateswhether or not he has heard this sound. The sound emitted can be madeup, for example, of three successive tonal bursts, each burst having aduration of 400 milliseconds, including advantageously raised cosineramps of 20 milliseconds; the three bursts being separated by aninterval of 200 ms. The frequency chosen can be 2000 Hz for example, andthe level 60 decibels.

[0023] If the sound has been heard by the subject, the level of thesignal is reduced by a certain quantity x in decibels (for example, 10dB). On the other hand; if this same sound has not been heard, the levelis increased by a quantity y in decibels (for example, 20 dB). The soundis then presented again, and the procedure is repeated, the quantities xand y being progressively reduced.

[0024] The criterion for stopping the procedure consists either ofreaching a minimum level, or of carrying out a sufficient and prefixednumber of inversions around the estimated threshold, or of reaching aprefixed minimum value.

[0025] When an estimate of this absolute auditory threshold at one givenfrequency is obtained, the measurement of the threshold at a subsequentfrequency commences. This subsequent test frequency is determined bymeans of a device identical to the preceding one, and following adichotomic procedure according to the following rules:

[0026] all the octave frequencies between 500 and 16,000 Hz (i.e. 500,1000, 2000, 4000, 8000 and 16,000 Hz) are tested, in a pseudo-randomorder, in order to avoid the effects of habituation or fatigue.

[0027] if, at the end of these measurements, no relative increase in thethreshold (i.e. a difference of more than 10 dB between the thresholdsmeasured at one or other of the different frequencies tested) has beenobserved, threshold measurements are carried out at intermediatefrequencies (one-half octaves), first about 4000 Hz, then at higherfrequencies and at lower frequencies.

[0028] if a relative increase in threshold is observed by the subject ata given frequency, threshold measurements are carried out more preciselyaround this frequency, commencing by testing the higher and lowerfrequencies, according to a half-octave octave interval, then thisfrequency step is reduced and the measurement procedure resumes at theintermediate frequencies.

[0029] the criterion for stopping the procedure consists of reaching aminimum frequency step value or another criteria making it possible toattest that a sufficiently high level of precision has been reached. Theabsolute auditory thresholds are successively measured in both ears bymeans of the operational phase described above.

[0030] A second operational phase (cf. stage B) consists of measuringthe perceived frequency of the tinnitus. This measurement of the levelof the tinnitus is carried out either by means of a dichotomous framingprocedure, or following an adjustment procedure. In the first case, anintermittent sound at a given frequency is emitted by the second meansinto at least one of the subject's ears. For example, this sound is madeup of three 1-second pulses, each separated by 1 second of silence andat a frequency of 2000 Hz. The subject's task is to indicate by means ofa response-box type interface whether this sound is higher or lowerpitched than, or of the same tonality as, the tinnitus. The subject alsohas the possibility of hearing the same sound again before deciding.

[0031] If the sound emitted is higher pitched, the frequency of the testsound is divided by a certain factor. On the other hand, if this samesound is lower pitched, the frequency of the test sound is multiplied bythe same factor. Then the procedure is repeated, the factor beingreduced each time the subject's response is reversed (and increased eachtime the subject gives the same response more than twice in succession)until the value of this factor reaches a prefixed minimum value or thesubject indicates that the test sound has the same tonality as thetinnitus.

[0032] According to an advantageous characteristic of the processaccording to the invention and by the effect of a generator implementingsaid process, the third means making it possible to adjust, at eachfrequency, the level of test sound on the basis of the results of themeasurement of the thresholds produced in the first stage, so that thislevel is maintained between 5 and 10 dB above the absolute threshold andis thus always approximately at the same perceived intensity as thetinnitus. This adjustment has the advantage of considerably facilitatingthe measurement of the tonal level of the tinnitus. In fact, theintensity being a crucial factor for the characterization of the levelof the tinnitus, by neutralizing the effect of the latter, it is easierto localize the frequency which corresponds to the level of thetinnitus.

[0033] After a first estimate of the tinnitus frequency has beenobtained, other successive measurements are carried out, until asufficient reproducibility criterion of the measurement has beenreached. Such a criterion consists, for example, of obtaining a 95%confidence interval having a range equal to or less than a required andpredefined minimum range around the estimated tonal level of thetinnitus.

[0034] In subjects who indicate that they perceive their tinnitus in oneear, the measurement of the level of the tinnitus according to theoperational phase described above is carried out successively with saidintermittent sound presented in this ear (ipsilateral matching), then inthe opposite ear (contralateral matching). In subjects who indicate thatthey perceive tinnitus centred in the intracranial space, the matchingsound is presented simultaneously in both ears, with the same phase. Insubjects who say that they perceive tinnitus localized in both ears, thematching of the tinnitus of each ear is carried out by presenting thetest sound in the same ear (ipsilateral matching).

[0035] At the end of this stage of tinnitus tonal level measurement, itis verified that this level falls into, or close to a frequency zone inwhich the absolute auditory thresholds are increased.

[0036] The third operational phase (cf. Stage C) consists ofdetermining, on the basis of the measurements obtained, thecharacteristics of an adapter-equalizer signal adapted to the particularcase of the subject.

[0037] Thus, starting with the data measured in the preceding stages,the spectral envelope still referred to as characteristic of the signalis calculated using algorithms in order to compensate for the hearingloss or losses measured in the first stage. Diagrammatically, thisenvelope corresponds to the negative (on the scale of ordinatesrepresenting a gain in intensity) of the tonal audiogram measured in thefirst stage: the amplitude of this envelope is greater in the regions inwhich the absolute auditory thresholds are highest.

[0038] The algorithmic formulae for the calculation of this envelope ofthe adapter-equalizer signal starting from the tonal audiogram are asfollows:

[0039] Let Ai be the absolute auditory thresholds (in decibels) at thedifferent frequencies Fi at which these thresholds have been tested, letAj be the absolute auditory thresholds at the frequencies Fj (estimatedby interpolation from the Ai's measured) with j belonging to the groupof integers [1; N] where N is the number of points in the spectralwindow, and let Fj=j*(Fe/N), Fe being the sampling frequency. Thespectral envelope of the adapter-equalizer signal at each point j of thespectral window is then calculated using the following mathematicalformula:

Ej=B+Mj−Qr(Aj)

[0040] where: B represents the minimum level of the adapter-equalizersignal; Mj=N−Aj where N is the average of the minimum thresholdsobtained with the tonal audiometry; and Qr(Aj) is a correction factorintroduced to take account of the effects of the cochlear compressionand reduction of frequency selectivity over the quantity of excitationproduced by the signal in the auditory system. FIG. 2 diagrammaticallyrepresents the spectral envelope of the adapter-equalizer signal thuscalculated from the absolute auditory thresholds.

[0041] Thus, and according to an advantageous characteristic of theprocess according to the invention, the characteristics of said auditorysignal as exactly as possible compensate for the subject's hearing loss,in order to eliminate the spectral contrasts in the activity of theauditory system which are caused by the hearing loss. In other words,this signal is intended to make the discontinuities in the activity ofthe neurons across the frequencies disappear. FIG. 3 represents, atseveral levels of the auditory system, neuronal responses evoked by suchan adapter-equalizer signal in the presence of a hearing loss. Bycomparison, FIG. 4 represents the same diagram of neuronal responsesevoked by a white noise used in the tinnitus-masking devices currentlyavailable on the market: with an adapter-equalizer signal calculated andprogrammed according to the invention and adapted to the particular caseof each subject, this is approximately level and constant, whereas witha white-noise-type signal, the neuronal activity always presents a peakat the level of the tinnitus frequency, which is interpreted as a soundby the central nervous system.

[0042] A characteristic of the present invention with respect to thesedevices (as well as those which, more generally, deliver a signal whosecharacteristics are not adapted to the individual's hearing loss) isthat the characteristics of the signal are determined on the basis of aprevious measurement of the precise form of the subject's hearing loss.

[0043] Moreover, only such a signal specifically adapted to the hearingof the subjects, subjected for a long enough period to the auditorysystem, leads, within the latter, to a reversal of the cerebralplasticity mechanisms following the appearance of the hearing loss, andassociated with the emergence and persistence of tinnitus. Thus, FIGS.5a to 5 c represent the tonotopic organization of the central neurons ina subject with normal hearing (FIG. 5a), in a subject with tinnitus withhearing loss (FIG. 5b) and in the same subject with tinnitus afterlistening to the adapter-equalizer signal for a sufficient period oftime (FIG. 5c). In these figures, the reference points 1 represent theneurons organized in tonotopic fashion (at a given position, a reducedfrequency band corresponds). In FIG. 5b, the neurons corresponding tothe hearing loss boundary 4 correspond to the adjacent frequencies: afrequency zone 2 is therefore found “over-represented” at the centrallevel (this zone corresponds to the frequency of the tinnitus). Asrepresented in FIG. 5c, the adapter-equalizer signal 5 then reverses theplasticity mechanisms induced by the hearing loss (normalization of thecentral tonotopic organization, reference point 3).

[0044] The fourth operational phase of the process according to theinvention and, incidentally, a characteristic of a generator allowingthe implementation of said process (cf. stage D) consists of thegeneration of the auditory signal or the fixation of this signal or ofits characteristics on a storage support for purposes of subsequentrestitution. In fact, once the characteristics of the adapter-equalizersignal have been calculated, this signal can, depending on the user'schoice, be generated directly in its temporal form (by multiplication ofthe spectral envelope with the spectrum of a white noise, then inverseFourier transform) for the purposes of direct use (for example byelectroacoustic transduction) or for the purposes of storage within adigital- or analogue-type support, chosen for example from compactdiscs, mini-discs, cassettes, hard discs, or floppy disks, this use orthis storage being obtained by appropriate means.

[0045] The characteristics of the signal can also be used to programmean electronic device included in these means (for example, aprogrammable memory containing coefficients characteristic of thetransfer function of a numeric filter, said coefficients can becalculated in particular by Z transformation) intended to participate inthe restitution of the signal by a device (for example a hearing aid ora device for generating acoustic signals fitted around the ear, or anintra-auricular device).

[0046] According to an advantageous characteristic of the invention, theprocess according to the invention comprises a final operational phase(cf. Stage E) which consists of adjusting, by interaction with thesubject, the intensity of the adapter-equalizer signal also calledcorrective signal. The latter must not totally mask the tinnitus andmust be of a sufficient intensity to optimize its effectiveness.

[0047] The minimum level of tinnitus maskability is automatically soughtusing an ascending procedure by virtue of which the level of the signalis progressively increased in order to avoid the phenomenon of residualinhibition. Once the masking threshold is obtained, the signal level isadvantageously adjusted between 5 and 10 dB below it.

[0048] The present invention as described previously, offers a number ofadvantages; in particular, it makes it possible to specifically adaptthe signal to the hearing loss of each patient suffering from tinnitus.The useful components of the signal (those located in the subject'shearing loss zone) being amplified with respect to those which falloutside the loss, the stimulation level can be lower than that used withthe devices which generate signals which are not as precisely adapted tothe subjects' hearing. This property confers greater listening comforton the adapter-equalizer signal. In fact, the lower the signal level,the less the individuals are disturbed in their daily activities.Moreover, the flexibility provided by the possibility of storing thesignal on any support that the patients can listen to by means of aWalkman or audio system at home or outside, provides considerablecomfort in use to these patients who are generally used to morerestrictive approaches.

[0049] Of course the present invention is not limited to the examples ofimplementation and embodiments described above, but it includes allvariants thereof.

1. Process for programming an auditory signal generator, with a view toalleviating, even eliminating tinnitus, characterized in that thefollowing operational phases are carried out: a) measurement of theabsolute auditory thresholds, b) calculation on the basis of themeasurements obtained, of the characteristics of an auditory signaladapted to a subject's particular case.
 2. Process according to claim 1,characterized in that it moreover comprises an intermediate stagebetween the main stages a and b corresponding to the measurement of theperceived frequency of the tinnitus.
 3. Process according to one ofclaims 1 or 2, characterized in that, in order to carry out saidmeasurement of the absolute auditory thresholds, the first means emitinto the right or left ear of a subject an intermittent sound of givenintensity and frequencies, of which the intensity and frequency arevaried depending on the responses given by said subject using a responsedevice, said subject having the task of indicating whether or not he hasheard said intermittent sound.
 4. Process according to one of claims 1to 3, characterized in that, in order to carry out said measurement ofthe perceived frequency of the tinnitus, the second means emit into theright and/or left ear of the subject an intermittent sound of givenfrequency, the frequency of which is varied depending on the responsesgiven by said subject using a response device, said subject having thetask of indicating whether said intermittent sound is higher pitched,lower pitched or of the same tonality as the tinnitus.
 5. Processaccording to any one of claims 1 to 4, characterized in that saidcalculation of the characteristics of said auditory signal is carriedout using algorithms.
 6. Process according to any one of claims 1 to 5,characterized in that a last operational phase is carried out, whichconsists of adjusting the intensity of said corrective signal so as tooptimize its effectiveness.
 7. Process according to claim 5,characterized in that said algorithms for calculating thecharacteristics of said auditory signal are: Ej=B+Mj−Qr(Aj) where B isthe minimum level of said auditory signal; Mj=N−Aj with N being theaverage of the minimum thresholds obtained and Aj the absolute auditorythresholds, and Qr(Aj) is a correction factor.
 8. Process according toany one of claims 1 to 7, characterized in that the characteristics ofsaid auditory signal are such that they compensate as exactly aspossible for a hearing loss.
 9. Generator allowing the implementation ofthe process according to any one of claims 1 to 8, characterized in thatit comprises first appropriate means allowing it to deliver saidcorrective signal comprising a device for multiplication of the spectralenvelope with the spectrum of a white noise and inverse Fouriertransform, for purposes of direct use or for purposes of storage withina support.
 10. Generator according to claim 9, characterized in thatsaid first appropriate means allowing it to deliver said correctivesignal comprises a programmable electronic device using thecharacteristics of said signal.
 11. Generator according to claim 9,characterized in that said storage support is of digital or analoguetype.
 12. Generator according to claim 10, characterized in that saidelectronic device is a programmable memory containing coefficientscharacteristic of the transfer function of a numeric filter, saidcoefficients being be calculated in particular by Z transformation. 13.Generator according to claim 12, characterized in that said programmablememory is integrated into a hearing aid or a device mounted around theear, or an intra-auricular device.
 14. Generator according to any one ofclaims 9 to 13, characterized in that the third means make it possibleto adjust, at each frequency, the level of said intermittent sound onthe basis of the results of said measurements of the absolute auditorythresholds, so that said level is of approximately the same perceivedintensity as the tinnitus.